二叉搜索树与双向链表

题目：输入一棵二叉搜索树，将该二叉搜索树转换成一个排序的双向链表。要求不能创建任何新的结点，只能调整树中结点指针的指向。

#include<iostream>

using namespace std;

struct BinaryTreeNode
{
	int val;
	BinaryTreeNode* left;
	BinaryTreeNode* right;
};

void ConvertNode(BinaryTreeNode* pNode, BinaryTreeNode** pLastNodeInList);

BinaryTreeNode* CreateTreeNode(int val)
{
	BinaryTreeNode* pNode = new BinaryTreeNode;
	pNode->val = val;
	pNode->left = nullptr;
	pNode->right = nullptr;
	return pNode;
}
//连接结点
void Connect(BinaryTreeNode* pRoot, BinaryTreeNode* left, BinaryTreeNode* right)
{
	if (pRoot != nullptr)
	{
		pRoot->left = left;
		pRoot->right = right;
	}
}
//释放结点
void DestroyTree(BinaryTreeNode* pRoot)
{
	if (pRoot != nullptr)
	{
		BinaryTreeNode* pLeft = pRoot->left;
		BinaryTreeNode* pRight = pRoot->right;
		delete pRoot;
		pRoot = nullptr;
		DestroyTree(pLeft);
		DestroyTree(pRight);
	}
}

BinaryTreeNode* Convert(BinaryTreeNode* pRoot)
{
	BinaryTreeNode* pLastNodeInList = nullptr;
	ConvertNode(pRoot, &pLastNodeInList);
	//pLastNodeInList返回的是链表最后一个结点，需要返回第一个结点
	BinaryTreeNode* pHeadOfList = pLastNodeInList;
	while (pHeadOfList != nullptr&&pHeadOfList->left != nullptr)
		pHeadOfList = pHeadOfList->left;
	return pHeadOfList;
}

void ConvertNode(BinaryTreeNode* pNode, BinaryTreeNode** pLastNodeInList)
{
	if (pNode == nullptr)
		return;
	BinaryTreeNode* pCurrent = pNode;
	//判断当前结点是否有左结点，有的话遍历它的左结点
	if (pCurrent->left != nullptr)
		ConvertNode(pCurrent->left, pLastNodeInList);
	//如果没有左结点，则把当前结点和它的前一个结点（即左结点）互相连接
	pCurrent->left = *pLastNodeInList;
	if (*pLastNodeInList != nullptr)
		(*pLastNodeInList)->right = pCurrent;
	*pLastNodeInList = pCurrent;
	//判断当前结点有没有右结点，有的话则继续连接右结点
	if (pCurrent->right != nullptr)
		ConvertNode(pCurrent->right, pLastNodeInList);
}

void PrintRight(BinaryTreeNode* pRoot)
{

	if (pRoot != nullptr)
	{
		BinaryTreeNode* pNode = pRoot;
		while (pNode != nullptr)
		{
			printf("%d\t", pNode->val);
			pNode = pNode->right;
		}
	}
}

int main()
{
	BinaryTreeNode* pNode1 = CreateTreeNode(1);
	BinaryTreeNode* pNode2 = CreateTreeNode(2);
	BinaryTreeNode* pNode3 = CreateTreeNode(3);
	BinaryTreeNode* pNode4 = CreateTreeNode(4);
	BinaryTreeNode* pNode5 = CreateTreeNode(5);
	BinaryTreeNode* pNode6 = CreateTreeNode(6);
	BinaryTreeNode* pNode7 = CreateTreeNode(7);
	BinaryTreeNode* pNode8 = CreateTreeNode(8);
	BinaryTreeNode* pNode9 = CreateTreeNode(9);

	Connect(pNode5, pNode3, pNode7);
	Connect(pNode3, pNode2, pNode4);
	Connect(pNode2, pNode1, nullptr);
	Connect(pNode7, pNode6, pNode8);
	Connect(pNode8, nullptr, pNode9);

	BinaryTreeNode* pHead = Convert(pNode5);

	PrintRight(pHead);

	DestroyTree(pNode1);

	return 0;

}